feat(lsp): Add TailwindCSS LSP server support

[sandiiarov]

Summary

This PR adds TailwindCSS Language Server support to OpenCode, enabling IDE-like features (autocomplete, hover info, diagnostics) for TailwindCSS projects.

Changes

• Added Tailwind LSP server configuration in packages/opencode/src/lsp/server.ts
• Auto-installs @tailwindcss/language-server when not found in system
• Supports .css, .html, .jsx, .tsx, .vue, .astro, .svelte, .scss, .less files
• Detects TailwindCSS projects via tailwind.config.* or postcss.config.* files
• Updated LSP documentation in packages/web/src/content/docs/lsp.mdx

Testing

Tested locally with:

• Opening supported files in Tailwind projects
• Verified LSP server spawns automatically
• Checked diagnostics for invalid Tailwind classes
• Tested auto-detection of config files

Fixes #8518